1. Field of the Invention
The present invention relates to a defect inspection method for manufactured products, and more particularly to a method for detecting defects in semiconductor products such as LSIs, TFTs, PDPs and thin-film display elements that require highly accurate defect detection, and relates to a method for evaluating these detected defects.
2. Description of the Related Art
As semiconductor design rules have become more detailed, the size of the manufacturing defects of semiconductor products has also become extremely small. The practice of detecting and reviewing defects by means of images detected using a conventional visible light source has grown difficult, and hence inspections and reviews of defects have come to be performed by using images detected by means of inspection devices employing DUV light as the light source, as well as images detected using SEM.
However, the increase in sensitivity afforded by using a DUV light source and SEM has frequently produced problems such as the detection of minute inconsistencies in the pattern not originally requiring detection, the detection of parts exhibiting thin film interference which is generated through the use of DUV light, the detection of locations which are targeted for charging by electrons that are emitted when an SEM image is picked up and so forth, or the detection of locations that were not originally defects.
As an example of a corresponding conventional technology, a method for determining, on the basis of localized correlations between a defect image and a reference image from inconsistencies in localized gray scale values generated between the defect image and the reference image, whether or not the resulting image constitutes a defect, is described in Japanese Patent Application Laid-Open No. 2001-77165, for example.
Furthermore, Japanese Patent Application Laid-Open No. 2000-105203 discloses a technology that involves calculating
scattering on the basis of the locations in which identical patterns were originally formed or of signals that are obtained through detection of regions in the vicinity of these locations, and then detecting defects from a signal detected on the basis of a determination reference which is established on the basis of the scattering thus calculated.
However, the above conventional technology has failed to adapt to the increased detail of the defects detected or to the increase in pattern detail.
For example, according to the technology disclosed by Japanese Patent Application Laid-Open No. 2001-77165, a correlation between the defect image and the reference image is found for each region in which the gray scale unevenness is different and then defects are detected on the basis of the correlations thus found. However, feature amounts such as texture and gray scale values, and so forth, are used as the means for performing segmentation into regions in which the gray scale unevenness is different. Consequently, reliable segmentation into regions in which the gray scale unevenness is different is problematic, no consideration having been paid to the problem that sections with varying degrees of gray scale unevenness belong within the same region, which is a possibility that results from such segmentation.
On the other hand, according to the method disclosed by Japanese Patent Application Laid-Open No. 2000-105203, although scattering is calculated on the basis of signals that are obtained by means of detection from regions in the vicinity of locations in which identical patterns were originally formed, this method does not take into consideration the elimination of grain effects which are most evident in the wiring step and so forth. Grains are a phenomenon that is clearly visible in the wiring step and constitute a phenomenon according to which there is a variation in the detected brightness of the wiring due to the wiring surface's possessing minute undulations. Grains are generated on the wiring alone, but are not limited by the generation, with the highest possible frequency, of a treatment with dispersion scattering amounts based on detection signals obtained from identical chip locations as described in Japanese Patent Application Laid-Open No. 2000-105203.
Although this problem is alleviated by enlarging the neighboring regions as per the above-described conventional technology, the problem exists that regions with different attributes then lie within neighboring regions. That is, in this grain example, even though there is a requirement to calculate the scattering of the original wiring pattern, the enlargement of the neighboring region results in the calculation of scattering that includes regions other than the wiring parts, which means that the scattering of the wiring pattern cannot be calculated. Hence, with the conventional technology, the higher the sensitivity of the inspection or defect observation method, the more locations that do not constitute defects are detected, and this technology has therefore been confronted by the problem that the detection and observation of the defects originally intended is problematic.
Furthermore, because the detection of defects is performed in one step, due to memory restrictions there is no other recourse but to assume that the calculation of scattering is performed using a Gaussian distribution and the like, and it has therefore not been possible to determine a complex scatter. Furthermore, because scattering using a Gaussian distribution is first found after an inspection of the entire wafer has been performed, it has not been possible to determine this scattering in the course of actually performing an inspection, and hence the threshold value could only be determined from the scattering at a point that lies several chips before the location ultimately inspected.